In light of the problem of ozone layer depletion that is a focus of attention in recent years, the restrictions on CFCs (chlorofluorocarbons) and HCFCs (hydrochlorofluorocarbons) that are used as refrigerants in conventional refrigerating machines have become more stringent, and HFCs (hydrofluorocarbons) are coming into use as substitute refrigerants.
Among HFC refrigerants, HFC-134a, R407C and R410A are routinely used as refrigerants for automobile air conditioners, refrigerators and room air conditioners. However, while these HFC refrigerants have ozone depletion potentials (ODP) of zero, their high global warming potentials (GWP) have led to their gradual restriction. Difluoromethane has been studied as an alternative to such refrigerants, but its global warming potential is not sufficiently low, while its boiling point is too low and its thermodynamic properties cannot be directly applied to current refrigeration systems, and it is poorly compatible with lubricating oils (refrigerating machine oils) such as polyol esters or polyvinyl ethers used with conventional HFC refrigerants. On the other hand, unsaturated fluorinated hydrocarbons have very low ODP and GWP and may be noncombustible depending on the structure, and include HFO-1234yf which is equivalent or superior to HFC-134a in terms of thermodynamic properties, as a measure of refrigerant performance, and therefore its use as a refrigerant has been proposed (Patent Literatures 1 to 3).